In order to correctly combust a fuel with air in a combustion chamber of a gas turbine the fuel and air/hot gas are usually supplied into one or more burners, which are located upstream of a combustion chamber; in the burner air/hot gas and fuel are mixed and the mixture is then combusted in a combustion chamber.
For a correct combustion (premixed combustion) mixing must be such that fuel and air/hot gas generate a homogeneous mixture, even with the constraints imposed by the space limitations of a burner of a gas turbine.
In order to quickly mix fuel and air/hot gas, the burners have a duct which includes structures creating turbulence. The air/hot gas passes through these structures acquiring turbulence; the fuel is injected in the turbulent flow such that quick mixing is achieved with the air/hot gas. In the following the structures creating turbulence are referred to as vortex generators.
EP 2 496 884 discloses vortex generators having walls with a substantially straight or curved leading edge and a trailing edge with a lobed shape.
U.S. Pat. No. 8,528,337 discloses nozzles with nozzle walls with a trailing edge having a first order lobed shape in turn defined by a second order lobed shape. For example FIG. 8 of U.S. Pat. No. 8,528,337 shows this arrangement.
The inventors have found a way to improve the performances in terms of mixing of the vortex generators of the kind described in EP 2 496 884.
In addition, since manufacturing of vortex generators whose trailing edge has more than one lobed shape is complex and expensive, in a particular embodiment the inventors have found a way to combine the advantages of vortex generators with first, second and possibly further order lobed shape with reduced manufacturing complexity and costs.